1. Field of the Invention
The present invention relates to methods for manufacturing nonreciprocal circuit devices, such as isolators, used in a high frequency region such as microwaves.
2. Description of the Related Art
The number of subscribers to mobile phones is continuously increasing, and in addition to the increase in new subscribers, replacement demand for new models is also increasing. Accordingly, devices necessary for the mobile phones are also increasingly required to have shorter delivery time and reduce cost. Nonreciprocal circuit devices used as isolators and the like, necessary devices in mobile phones, also need to satisfy the requirements described above.
Conventionally, a lumped-constant type circulator is composed of a plurality of central conductors which are located adjacent to a ferrite plate and are disposed so as to cross each other, a magnet applying a DC magnetic field to the ferrite plate, and a case receiving the elements described above therein. In addition, an isolator is formed by a resistor termination at a predetermined port among three ports of the circulator.
The central conductor constituting the nonreciprocal circuit device described above is conventionally formed by etching or punching a metal foil. However, when the central conductors are manufactured by an etching method, the manufacturing time is long because of a complicated etching process, and the lead time from order entry to delivery is long, whereby smooth delivery cannot be performed when production volume is suddenly increased. In addition, there are problems in that the manufacturing cost is high, and cost reduction is difficult to preform. Furthermore, in the etching process, variation in line widths of circuits, such as, a trapeziform cross-section of line width, is likely to occur because of a so-called over-etching, under-etching, or the like, and as a result, variation in performances of the nonreciprocal circuit devices may occur in some cases.
On the other hand, when the central conductors are manufactured by a punching method, compared to the etching method, advantages can be obtained in that the manufacturing time is shorter, the cost can be reduced, variation in line widths is smaller, and hence, variation in performances of the nonreciprocal circuit device can be reduced. However, a problem may arise in that when the central conductors itself are delivered, breakage or bending is likely to occur during transportation. In addition, when the central conductors are fed to a manufacturing step using an automatic machine, a plurality of central conductors must be aligned beforehand, and the time required for alignment is long, whereby the advantage, which can be obtained by using the automatic machine, is reduced by half.
Accordingly, an object of the present invention is to provide a method for manufacturing a nonreciprocal circuit device which can solve the problems occurred in an etching method and in a punching method, can significantly improve the productivity, and can manufacture a nonreciprocal circuit device having excellent performances.
According to this present invention, in a method for manufacturing a nonreciprocal circuit device comprising a magnetic body to which a DC magnetic field is applied, central conductors disposed adjacent to the magnetic body, and a case containing the magnetic body and the central conductors, the method comprises the steps of punching a metal foil in a hoop form by a die so as to form the central conductors for a plurality of the nonreciprocal circuit devices which are integrated, separating the central conductors from the metal foil in the hoop form, disposing the central conductors adjacent to the magnetic body, and placing the central conductors and the magnetic body in the case.
As described above, when the central conductors for the plurality of the nonreciprocal circuit devices are formed in an integrated state by punching the metal foil in the hoop form, the occurrence of the breakage and bending of the central conductors during transportation is prevented, and when the central conductors are fed into a manufacturing step by an automatic machine, the central conductors aligned beforehand can be fed thereinto.
In addition, according to the present invention, the metal foil may comprise at least one of the elements selected from a group consisting of iron, copper, and aluminum, and a metal film having a resistivity of 5.5 xcexcxcexa9xc2x7cm or less may be provided on the metal foil. In this structure, the breakage and bending of the central conductors are unlikely to occur even when a thin metal foil is used, and in addition, the conductor loss can also be reduced.
In the present invention, the metal foil may be a flat-rolled copper foil. In this case, the conductor loss can be further reduced by making the obverse and reverse surfaces of the metal foil smooth, and even when the thickness thereof is deceased, a strength at a certain level can be maintained.
Furthermore, according to the present invention, the method for manufacturing the nonreciprocal circuit device may further comprises the steps of forming the central conductors extending in radial directions from a stage on which the magnetic body is placed, bending the central conductors so as to wrap around the magnetic body, and insulating between the central conductors overlapped with each other by bending with insulating sheets, wherein a base material of the insulating sheet comprises at least one of the elements selected from a group consisting of a polyimide, a polyester, an aramid, a polyamide-imide, and a fluorinated resin, and the base material has a thickness of 0.05 mm or less. Consequently, the overall thickness of the nonreciprocal circuit device including the insulating sheets can be decreased, and the electrical insulating state between the central conductors overlapped with each other can be reliably maintained.